Well, I have a very reliable system in credit making and saving and it's simple, never fall below 10,000 credits.
When we built Virtual Splash Mountain, I had about 40,000 to build with along with the build team I've formed who all use the same system.
Then after, we built Virtual Big Thunder (which was a flop

) it put me a little over 12,000 (I posted that amount)..
I save nonstop for the arrival of Magic Carpet but after reading it might not show up till 2006 and with all this new stuff available, I may just have to settle for an 8,000 system.. which I hate to do, but now with the lame mansion game, reaching 100,000 credits is not too far off in the distance.